The invention relates to inverted mesa-type piezoelectric vibration pieces, and piezoelectric vibration devices using the same.
With increasingly higher frequencies in, for example, frequencies in communication devices and operating frequencies in microcomputers, it is necessary for piezoelectric vibration devices, such as crystal vibrators, crystal filters, and crystal resonators, to likewise meet the demand for higher frequencies. The piezoelectric plates configured for higher frequencies, which are typically used, are AT-cut crystal plates featured by thickness slip vibration, and the frequencies of such are, as is all too well known, decided by the thicknesses of crystal plates. Since the frequencies and thicknesses are in inverse proportion, the crystal plates are desirably ultrathin in thickness. To process the crystal plates in extremely small thicknesses needs a complicated grinding work, resulting in poor yields in the production of piezoelectric vibration pieces.
To deal with this problem, the patent document 1 discloses a piezoelectric vibration device with a generally called inverted mesa-type piezoelectric vibration piece.
In such an inverted mesa-type piezoelectric vibration device structurally advantageous in that driving electrodes and extraction electrodes are formed on surfaces of a thinned portion of a piezoelectric plate provided in the piezoelectric vibration piece, a vibration region can be significantly reduced in thickness, which enables the piezoelectric vibration device to attain higher frequencies.
FIG. 17 is a sectional view of a primary portion of the inverted mesa-type piezoelectric vibration device.
A piezoelectric vibration device 50 illustrated in the drawing has a piezoelectric vibration piece 51. The piezoelectric vibration piece 51 has an inverted mesa-type piezoelectric plate (crystal plate) 52 made of crystal. The piezoelectric plate 52 is provided with a thinned portion (vibration region) 52a rectangular in planar view at its central part, and a thickened portion 52b formed around the thinned portion 52a to reinforce the vibration region.
On the upper and lower surfaces of the thinned portion 52a of the piezoelectric plate 52 are arranged driving electrodes, which are respectively extracted by extraction electrodes to end parts on the upper surface of the thickened portion 52. Of these extraction electrodes, the drawing illustrates an extraction electrode 54 formed on the upper surfaces of the thinned portion 52 and the thickened portion 52b, and an end part 54a thereof.
A package 53 is in the form of a shallow box with an open upper surface constructed of a bottom portion 53a rectangular in planar shape and a peripheral wall portion 53b formed around the bottom portion 53a. 
The package 53 for housing the piezoelectric vibration piece 51 has, on its bottom part 53a, an internal terminal 55 in electrical continuity with an external terminal not illustrated in the drawing. The lid of the package 53 is not illustrated in the drawing.
The internal terminal 55 is pre-coated with a conductive adhesive s11. A connection electrode 56 on the lower surface of the thickened portion 52b is electrically and mechanically connected through the conductive adhesive s11 to the internal terminal 56.
An end part 54a of the extraction electrode 54 on the piezoelectric plate 52 is electrically and mechanically connected through a conductive adhesive s12 to the internal terminal 55.
The conductive adhesives s11 and s12 are adhesives in pasty form having flow properties, which are obtained by, for example, mixing a silicon-based adhesive with a solvent medium and a metallic filler such as silver. These adhesives are applied to their targets by a coating tool such as a dispenser or any other suitable tool.
The conductive adhesives s11 and s12 are thermally cured when heated to temperatures equal to or higher than a predetermined temperature. By thermally curing these adhesives, the end part 54a of the extraction electrode 54 is fixedly connected electrically and mechanically to the internal terminal 55.
The thermal curing is performed in, for example, a heating furnace. The piezoelectric vibration device 50, after the conductive adhesives s11 and s12 are applied thereto on the outside of the heating furnace, is put in the heating furnace to thermally cure the adhesives.
JP 4241483 B1 is related art.